Wastewater treatment with alkanes

ABSTRACT

An apparatus and method are provided for treating wastewater with alkanes such as butane. An oxygen-containing gas may also be introduced into the wastewater. Butane, because of its relatively high solubility, rapidly dissolves in the wastewater, thereby significantly increasing the heterogeneous microbial community and heterotrophic microbial population. This enhanced microbial population may rapidly absorb and mineralize materials in the wastestream. After an initial growth phase, the organic matter available in the wastewater effluent may be rapidly decreased, thereby reducing the amount of BOD, TDS, sludge and other pollutants. In addition, the use of butane reduces noxious odors associated with municipal wastewater sludges and other types of wastewater.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/291,165 filed May 15, 2001, which isincorporated herein by reference. This application is acontinuation-in-part of U.S. application Ser. No. 09/729,039 filed Dec.4, 2000, now U.S. Pat. No. 6,488,850 issued Dec. 3, 2002, which claimsthe benefit of U.S. Provisional Patent Application Serial No. 60/234,482filed Sep. 22, 2000. The 09/729,039 application is acontinuation-in-part of U.S. application Ser. No. 09/275,320 Mar. 24,1999, now U.S. Pat. No. 6,245,235 issued Jun. 12, 2001, which is acontinuation-in-part of U.S. application Ser. No. 08/767,750 filed Dec.17, 1996, now U.S. Pat. No. 5,888,396 issued Mar. 30, 1999.

FIELD OF THE INVENTION

The present invention relates to the treatment of wastewater, and moreparticularly relates to the use of alkanes to aerobically and/oranaerobically treat municipal, agricultural and industrial wastewater.

BACKGROUND INFORMATION

Liquid wastes are produced by most human activities including domesticsewage, agricultural processes and industrial operations. For example,according to the U.S. Department of Commerce, industrial water usersdischarge approximately 285 billion gallons of wastewater daily.

Some types of conventional wastewater treatment processes aremicrobiologically mediated. Municipal, agricultural and industrialwastewater is often treated aerobically, thereby converting pollutantsinto environmentally acceptable analogues. The addition of micro-bubblesof oxygen has been demonstrated to be an effective enhancement of theaerobic treatment of wastewater to lower biological oxygen demand (BOD),total dissolved solids (TDS) and total organic carbon (TOC).

Anaerobic wastewater treatment methods have also been used. For example,the addition of hydrogen has been found to enhance anaerobic processes,and to reduce unsaturated organic liquids and sludges. Anaerobicdigestion is one of the oldest processes used for the stabilization ofsludges. It involves the decomposition of organic matter and inorganicmatter in the absence of molecular oxygen. During conventional anaerobicdigestion, the organic matter in mixtures of primary settled andbiological sludges is converted biologically, under anaerobicconditions, to produce methane (CH₄) and carbon dioxide (CO₂). Duringconventional anaerobic digestion, a consortium of organisms convertsorganic sludges and wastes. One group hydrolyzes organic polymers andlipids. A second group of anaerobic bacteria ferments the breakdownproducts to simple organic acids. A third group of microorganismsconverts the hydrogen and acetic acid to methane gas and carbon dioxide.

Gas-liquid mixing systems are used in various processes and methodsemployed in the wastewater industries. Many types of mechanical devicesand mixers have been developed to improve wastewater treatment byenhancing gas-liquid mixing. By enhancing gas-liquid mixing, wastewateraerobic treatment processes are improved through increased oxygen(aerobic) and hydrogen (anaerobic) dissolution and residence time.

U.S. Pat. Nos. 5,916,491 and 5,925,290, which are incorporated herein byreference, disclose apparatus and methods for mixing gas and liquidthrough vortex or venturi devices. The mixers are particularly suitedfor mixing oxygen-containing gases into industrial and municipalwastewater. Other types of gas-liquid mixers are also disclosed in U.S.Pat. Nos. 3,969,446, 4,328,175, 4,454,077, Re. 32,562, 4,645,603,4,695,378, 4,956,080, 5,061,406, 5,073,309, 5,085,809, 5,314,076 and5,494,576, which are incorporated herein by reference.

The bioremediation of various pollutants such as chlorinated solventsand other types of pollutants using butane-utilizing bacteria isdisclosed in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372, 6,156,203and 6,210,579, which are incorporated herein by reference.

SUMMARY OF THE INVENTION

In accordance with the present invention, alkanes, e.g., methane,ethane, propane and butane, can be used to effectively degradepollutants and other materials typically found in wastewater such aschemical, industrial and municipal effluents. In a preferred embodiment,butane, having the highest solubility of the alkanes, can be used tocontrol BOD, TOC and TDS, as well as pollutants typically found inwastewater through enhanced growth of aerobic and/or anaerobic bacteria,and possibly other microorganisms that oxidize or reduce dissolvedorganic matter and sludge effluents, thereby significantly decreasingthe BOD of a wastestream.

Alkanes, preferably butane, may be used under aerobic and/or anaerobicconditions to enhance wastewater treatment processes during primary,secondary or tertiary treatment. Butane is highly soluble and ideallysuited to serve as a microbial growth substrate, thereby significantlyincreasing the heterogeneous microbial community and total heterotrophicmicrobial population found in wastewater. This enhanced microbialpopulation may rapidly absorb and mineralize the dissolved organicnutrients in the wastestream. To accelerate the dissolved organicnutrient reductions, the butane may be pulsed in the wastestream tocreate feeding frenzy/starvation cycles. After the initial growth phase,the organic matter available in the wastewater effluent may be rapidlydecreased thereby reducing the BOD, TOC and TDS.

An aspect of the present invention is to provide a method of treatingwastewater comprising introducing at least one alkane into thewastewater.

Another aspect of the present invention is to provide a method oftreating material contained in wastewater. The method comprisesstimulating growth of alkane-utilizing bacteria, and allowing thealkane-utilizing bacterial to degrade at least a portion of thematerial.

A further aspect of the present invention is to provide an apparatus fortreating wastewater comprising means for introducing at least one alkaneinto the wastewater.

Another aspect of the invention is to provide an apparatus for treatingwastewater comprising a wastewater containment vessel, and at least onealkane injector in flow communication with the wastewater containmentvessel.

These and other aspects of the present invention will be more apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic side view of an alkane aerobic digesterin accordance with an embodiment of the present invention.

FIG. 2 is a top view of the alkane aerobic digester of FIG. 1.

FIG. 3 is a partially schematic side view of an alkane anaerobicdigester in accordance with an embodiment of the present invention.

FIG. 4 is a top view of the alkane anaerobic digester of FIG. 3.

FIG. 5 is a partially schematic side view of a gas-liquid mixerincluding an alkane injection system in accordance with an embodiment ofthe present invention.

FIG. 6 is a partially schematic side view of a gas-liquid mixerincluding an alkane injection system in accordance with anotherembodiment of the present invention.

FIG. 7 is a top view of the gas-liquid mixer of FIG. 6.

FIGS. 8a and 8 b are schematic diagrams illustrating a butane-enhancedwastewater treatment process in accordance with embodiments of thepresent invention.

FIG. 9 is a schematic diagram illustrating a butane-enhanced wastewatertreatment process in accordance with another embodiment of the presentinvention.

FIG. 10 is a partially schematic side view of a bioreactor used to treatmunicipal wastewater sludge with butane in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION

In accordance with the present invention, aerobic and/or anaerobicdigestion with alkane-utilizing bacteria is used to treat wastewatermaterials, such as organic sludges produced from various treatmentprocesses. In accordance with a preferred embodiment of the presentinvention, butane, which has relatively high solubility, rapidlydissolves in wastewater, thereby significantly increasing heterogeneousmicrobial communities and heterotrophic microbial populations. Butane isa low molecular weight organic compound ideally suited to serve as amicrobial food substrate under aerobic and/or anaerobic conditions.Butane is non-toxic and may be added, for example, as an amendment in aprimary settling tank, aeration tank or secondary settling tank.

In accordance with an embodiment of the present invention, a butanesubstrate may be added to the wastewater to be treated. A preferredembodiment of the present invention relates to the treatment ofwastewater BOD, TDS and sludge. For example, a butane substrate may beinjected into the wastewater in a large treatment vessel equipped withoxygen injectors and turbulent mixing devices. The butane substrate maybe provided in any desired form, such as a liquid or gas injected intothe wastewater, or within a capsule that dissolves in the wastewater.

As used herein, the term “butane substrate” includes liquids and gasesin which butane is present in sufficient amounts to stimulate growth ofbutane-utilizing bacteria. Butane is preferably the most prevalentcompound of the butane substrate on a weight percent basis, andtypically comprises at least about 10 weight percent of the butanesubstrate. The other constituents of the butane substrate may includeany suitable compounds, including inert gases and/or other alkanes suchas methane, ethane and propane. The butane substrate preferablycomprises at least about 50 weight percent butane. More preferably, thebutane substrate comprises at least about 90 weight percent butane. In aparticular embodiment, the butane substrate comprises at least about 99weight percent n-butane. The butane may contain straight (n-butane)and/or branched chain compounds.

Oxygen may be introduced into the wastewater during at least a portionof the treatment time. As used herein, the term “oxygen-containing gas”means gases which comprise oxygen, including pure oxygen as well asmixtures of oxygen with other gases. For example, the oxygen-containinggas may comprise air, pure oxygen, or oxygen blended with inert gasessuch as helium, argon, nitrogen, carbon monoxide or the like.

Although the use of a butane substrate is primarily described herein, itis to be understood that other alkanes, i.e., methane, ethane and/orpropane, may be used in addition to, or in place of, butane. Forexample, natural gas may be used as a food source. Furthermore,alternative food sources may be used in addition to, or in place of, thealkanes. Examples of alternate food sources include agars, simple andcomplex sugars, carbohydrates, carbon sources, milk products, eggalbumin, egg products, blood serums, urea, urea broth, beet molasses,glucose, xylose and glucose, xylose, mannose, lactate, mannitol, yeastextract, sorbitol, wheat bran, straw, molasses, cereals, corn, potatostarch, corn cob, fish meal, grain, gelatin, corn steep liquor, cornmeal, nutrient gelatin, rice bran, casein hydrolysate, ethanol,agricultural residues, peat moss hydrolysate, lactose, sugar-cane syrup,synthetic ethanol, gasoline, petroleum distillates, aliphatic andaromatic hydrocarbons, non-petroleum compounds, fructose, fatty acids,proteins, cellulose, engineered biological fuel components,nitrates/nitrites/ammonia, maltose, sucrose, starch, acetate, glycerol,soluble starch, amino acids, casamino acids, meat extracts, organicacids, barley, barley malt, blood meal, cane (black strap) molasses,cerelose, CFS concentrate, corn gluten meal, cotton seed meal, drieddistillers' solubles, edamine, enzose, fermamin, fish solubles, fishmeal, linseed meal, meat and bone meal, NZ-Amine B, oat flour, peanutmeal and hulls, pharmamedia, rice flour, soybean meal, wheat flour, wheypowder, brewers' yeast, yeast hydrolysate, yeast tortula, arabinose,fumarate, pyruvate, succinate, phosphate, galactose, glycol, crotonate,glutamate, arginine, ribose, methanol, propanol, fuel oils, all volatilepetroleum hydrocarbons (VPH) and all extractable petroleum hydrocarbons(EPH) including the C₅-C₈ aliphatic range, C₉-C₁₂ aliphatic range,C₉-C₁₀ aromatic range, C₁₁-C₂₂ aromatic range, C₉-C₁₈ aliphatic range,C₁₉-C₃₆ aliphatic range, C₃₆ and higher aliphatic range, benzene,toluene, ethylbenzene, xylenes, naphthalene, polynuclear (1, 2, 3 ringsand higher) hydrocarbons (PAHs), butyrate, butylaldehyde, butanol,1-butanol, 2-butanol, pentane, nonane, styrene, octane, n-octane,organic compounds, alcohols, hexadecanol, ethylene glycol, microbialmetabolites, carboxylic acids, acids, such as formic, acetic, propionic,oxalic, acrylic, methacrylic, mineral spirits, mineral oils, petroleumjellies, aldehydes, mushroom extracts, mushrooms, aliphatic amines,aromatic amines, ethers, aliphatic and aromatic esters, glycol ethers,ketones, grain dust, phenols, cheese whey, gas oils, cellulose-pulping,carbon dioxide, gas and oil, carob bean extract, waste starch,fermentation products, endogenous oxidized cell tissue, high molecularmass compounds, cell protoplasm, dead microbial cells, wood, wood chips,sawdust, coal and coal dust.

In accordance with a preferred embodiment, butane availability resultsin the selection of robust and diverse microbial populations. Theseenhanced microbial populations may rapidly absorb and mineralize thedissolved organic nutrients in the wastestream. After this initialgrowth phase, the organic matter available in the wastewater effluentwill be rapidly decreased thereby reducing the BOD, TDS and sludgecomponents.

Typically, during aerobic digestion, in a process known as endogenousrespiration, as an available food substrate is depleted, themicroorganisms begin to consume their own protoplasm to obtain energyfor cell maintenance reactions as shown by the following equation:

For example, if activated or trickling filter sludge is mixed withprimary sludge and the combination is to be aerobically digested, therewill be both direct oxidation of the organic matter in the primarysludge and endogenous oxidation of the cell tissue as the readilyavailable organic matter is depleted. One consequence of butaneavailability in a wastestream, e.g., by cycling or pulsing, is toaccelerate oxidation of the organic matter by reducing endogenousrespiration. Another benefit of butane availability is the direct resultof the increase in cell densities and the microbiological diversityresulting under butane tension. This increased microbiological communitywill further enhance organic matter digestion.

The butane aerobic digesters may be used, for example, to treatwaste-activated or trickling-filter sludge, mixtures of waste-activatedor trickling-filter sludge and primary sludge, and/or waste sludge fromactivated-sludge treatment plants designed without primary settling.

In addition to dissolved solids removal, the butane/oxygen process maybe used to accelerate sludge decomposition and reduction. High oxygenconcentrations may be maintained for microbial proliferation and toreduce bulking of the sewage sludge. For example, by retrofittingexisting conventional wastewater treatment tanks, a butane aerobicdigester may be added into the process flow during any stage of theoverall treatment process. Settled and dissolved biomass may becontinuously recycled to maximize the rate of aerobic digestion. Sincemany wastewater facilities include aeration tanks equipped with mixersand air and/or oxygen injection diffusers, the system retrofit maysimply include the addition of butane injectors such as ports and/ordiffusers. Likewise, conventional anaerobic digesters may be convertedto butane anaerobic digesters through the addition of butane injectors.

In accordance with an embodiment of the present invention,alkane-utilizing bacteria may be used to anaerobically treat wastewatermaterials. For example, butane may serve as an electron donor to degraderecalcitrant compounds under anaerobic conditions through reductivedechlorination processes. Under anaerobic conditions, butaneavailability may increase enzyme-mediated biotransformations, such thathigher-molecular-mass compounds are converted into compounds suitablefor use as a source of energy and cell carbon. Butane may thus serve asan electron donor to degrade recalcitrant compounds under anaerobicconditions.

FIG. 1 is a partially schematic side view of an aerobic butane digester10 in accordance with an embodiment of the present invention. FIG. 2 isa plan view of the aerobic butane digester 10 shown in FIG. 1. Thedigestor 10 includes a vessel 12 which contains wastewater 14. Awastewater feed line 16 feeds the wastewater into the vessel 12. Asolids removal line 18 permits the removal of solids and other materialsfrom the vessel 12. An impeller 19 is mounted in the vessel 12. Analkane injection line 20 is connected to diffusers 22 inside the vessel12. An oxygen-containing gas injection line 30 is connected to diffusers32 inside the vessel 12. As shown most clearly in FIG. 1, duringoperation of the aerobic butane digestor 10, the impeller 19 is rotatedin order to circulate the wastewater 14 within the vessel 12. The alkaneand oxygen-containing gas are introduced into the wastewater 14 throughthe diffusers 22 and 32, respectively. The alkane is typicallyintroduced in the wastewater 14 in pulses or intervals. Theoxygen-containing gas may be injected into the wastewater 14continuously or intermittently.

FIGS. 3 and 4 are partially schematic side and plan views, respectively,of an anaerobic butane digestor 34 in accordance with an embodiment ofthe present invention. The anaerobic butane digestor 34 shown in FIGS. 3and 4 is similar to the digestor shown in FIGS. 1 and 2, except theoxygen-containing gas injection lines are replaced with additionalalkane injection lines 20. The anaerobic butane digestor 34 alsoincludes a vent line 36. During operation of the anaerobic butanedigestor 34, the impeller 19 likewise rotates to circulate thewastewater 14, while the alkane is introduced into the wastewater 14with the diffusers 22. The alkane may be introduced into the wastewater14 continuously intermittently.

In addition to the embodiments shown in FIGS. 1-4, conventionalgas-liquid mixers may be adapted or modified to allow for the injectionof butane or other alkanes into the treatment zone. For example,gas-liquid mixers as disclosed in U.S. Pat. Nos. 5,916,491 and 5,925,290may be modified to introduce butane at any desired location(s) in theliquid stream, for example, inside the draft tube of the mixers.

FIG. 5 is a partially schematic side view of a gas-liquid mixer 50including an alkane injection system 40 in accordance with an embodimentof the present invention. The alkane injection system 40 includes analkane cylinder 42 and an inert gas cylinder 44 which may contain a gassuch as helium. A regulator 46 is connected between the alkane cylinder42 and the inert gas cylinder 44. An alkane injection line 48 connectsthe alkane injection system 40 to the mixer 50. The mixer 50 includes awastewater containment vessel 51. A draft tube 52 and an impeller 53 arepositioned in the wastewater containment vessel 51. A conical inletbaffle 54 is located at the top of the draft tube 52, while an outletbaffle 55 is located at the bottom of the draft tube 52. An airinjection line 58 extends into the draft tube 52 below the conical inletbaffle 54. During operation of the system shown in FIG. 5, rotation ofthe impeller 53 draws wastewater vertically downward through the drafttube 52. Alkanes delivered through the injection line 48 and airdelivered through the air injection line 58 mix with the wastewaterinside the draft tube 52.

FIG. 6 is a partially schematic side view and FIG. 7 is a top view of agas-liquid mixer including an alkane injection system 40 in accordancewith another embodiment of the present invention. The alkane injectionsystem 40 shown in FIGS. 6 and 7 is similar to the system shown in FIG.5. In the embodiment shown in FIGS. 6 and 7, the gas-liquid mixer 60includes a wastewater containment vessel 61 having a draft tube 62 withan impeller 63 mounted therein. An inlet baffle 64 is mounted at the topof the draft tube 62, while an outlet baffle 65 is mounted at the bottomof the draft tube 62. During operation of the mixer 60 shown in FIGS. 6and 7, rotation of the impeller 63 draws the wastewater through thedraft tube 62, and also causes air-filled vortices to form, therebyentraining air as the wastewater is drawn through the draft tube 62.Alkanes fed through the alkane injection lines 48 are also entrained inthe wastewater as it is drawn through the draft tube 62.

FIG. 8a is a schematic diagram illustrating a butane-enhanced wastewatertreatment process in accordance with an embodiment of the presentinvention. In the embodiment shown in FIG. 8a, butane-enhanced odorcontrol is achieved by introducing butane into the wastewater prior tothe primary settling tank. After the primary settling tank, thewastewater may flow to a butane-enhanced aeration tank, then to a beltfilter press. In addition, wastewater from the primary settling tank maybe fed to a butane-enhanced aeration tank for secondary treatment. Inthe secondary treatment stage, return activated sludge is fed to thebutane-aeration tank and then to a final settling tank. After the finalsettling tank, the wastewater may be fed to a chlorine contact tankand/or another butane-enhanced aeration tank. The embodiment shown inFIG. 8b is similar to the embodiment shown in FIG. 8a, except thesecondary treatment stage includes a standard aeration tank, rather thana butane-enhanced aeration tank.

FIG. 9 is a schematic diagram illustrating a butane-enhanced wastewatertreatment process in accordance with another embodiment of the presentinvention. In the embodiment shown in FIG. 9, wastewater undergoesbutane-enhanced odor control before it is fed to a primary settlingtank. A secondary treatment stage similar to that shown in FIG. 8b isused, except the final settling tank is connected to a gravitythickener. Wastewater exiting the gravity thickener is fed to ananaerobic digestor, followed by a butane-enhanced aeration tank. Aftertreatment in the butane-enhanced aeration tank, the wastewater is fed toa belt filter press. Some of the material from the gravity thickener,anaerobic digestor, butane-enhanced aeration tank and belt filter pressmay be recycled to the primary settling tank.

The butane injection processes may be used to treat BOD, TOC, ammonia,nitrates, nitrites, phosphorus, total organic carbon, organic andmineral settleable and nonsettleable suspended solids, organic andmineral colloidal and dissolved filterable solids and sludge. Forexample, the butane/air process will treat sludge and solidscontaminated with nitrogen-based aromatics (explosives), PCBs,pesticides, chlorinated aliphatic and aromatic compounds, aliphatic andaromatic hydrocarbons, and PAHs, esters, ethers, aldehydes, amines,dioxin-and related compounds, herbicides, ketones, phenols,sulfur-containing organics and alcohols, ethylene dibromide (EDB),chlorophenolic compounds (chlorophenols, chloroguiacols, andchlorocatechols, pulp mill effluent, low-level radioactive wastes,chlorate (pulp bleaching), cyanide, arsenic, chromium, copper, iron,lead, and other metals.

Some of the pollutants which may be degraded by the present system andmethod include chlorinated aliphatics, chlorinated aromatics andnon-chlorinated aromatics and aliphatics, with chlorinated aliphatichydrocarbons being of particular interest. Specific hydrocarbonpollutants include trichloroethene (TCE), trichloroethane (TCA) (e.g.,1,1,2-trichloroethane and 1,1,1-trichloroethane), methylene chloride,1,1-dichloroethane, chloroform, 1,2-dichloropropane,dibromochloromethane, 2-chloroethylvinyl ether, tetrachloroethene (PCE),chlorobenzene, 1,2-dichloroethane, bromodichloromethane,trans-1,3-dichloropropene, cis-1,3-dichloropropene, bromoform,chloromethane, bromomethane, vinyl chloride, chloroethane,1,1-dichloroethene, trans-1,2-dichloroethene, methyl tertiary butylether (MTBE), polychlorinated biphenyl (PCB), dichlorobenzenes,cis-1,2-dichloroethene, dibromomethane, 1,4-dichlorobutane,1,2,3-trichloropropane, bromochloromethane, 2,2-dichloropropane,1,2-dibromoethane, 1,3-dichloropropane, bromobenzene, chlorotoluenes,trichlorobenzenes, trimethylbenzenes, trans-1,4-dichloro-2-butene andbutylbenzenes. Additional pollutants include petroleum compounds such ascrude oil, refined oil, Nos. 2, 4 and 6 fuel oils, gasoline, benzene,toluene, ethylbenzene and xylene (BTEX), and creosote.

Facultative anaerobes and microaerophilic bacteria are capable ofsurviving at low levels of oxygen. They do not require strict anaerobicconditions such as the obligate anaerobes. Acidophilic, alkaliphilic,anaerobe, anoxygenic, autotrophic, chemolithotrophic, chemoorganotroph,chemotroph, halophilic, methanogenic, neutrophilic, phototroph,saprophytic, thermoacidophilic, and thermophilic bacteria may be used.

Wastewater treatment processes that may be used in accordance with thepresent invention include the use of butane-utilizing microorganismswhich may be found naturally in wastewater. Bacteria may include thefollowing Groups (in addition to fungi, algae, protozoa, rotifers andall other microbial populations found in municipal, agricultural andindustrial wastewaters.)

Group 1 The Spirochetes Group 2 Aerobic/Microaerophilic, motile,helical/vibroid, gram-negative bacteria Group 3 Nonmotile (or rarelymotile), gram-negative bacteria Group 4 Gram-negativeaerobic/microaerophilic rods and cocci Group 5 Facultatively anaerobicgram-negative rods Group 6 Gram-negative, anaerobic, straight, curved,and helical bacteria Group 7 Dissimilatory sulfate- or sulfur-reducingbacteria Group 8 Anaerobic gram-negative cocci Group 10 Anoxygenicphototrophic bacteria Group 11 Oxygenic phototrophic bacteria Group 12Aerobic chemolithotrophic bacteria and associated organisms Group 13Budding and/or appendaged bacteria Group 14 Sheathed bacteria Group 15Nonphotosynthetic, nonfruiting gliding bacteria Group 16 The fruiting,gliding bacteria and the Myxobacteria Group 17 Gram-positive cocci Group18 Endospore-forming gram-positive rods and cocci Group 19 Regular,nonsporing, gram-positive rods Group 20 Irregular, nonsporing,gram-positive rods Group 21 The mycobacteria Groups 22-29 Theactinomycetes Group 22 Nocardioform actinomycetes Group 23 Genera withmultiocular sporangia Group 24 Actinoplanetes Group 25 Streptomycetesand related genera Group 26 Maduromycetes Group 27 Thermomonospora andrelated genera Group 28 Thermoactinomycetes Group 29 Genus Glycomyces,Genus Kitasatospira and Genus Saccharothrix Group 30 The Mycoplasmas -cell wall-less bacteria Group 31 The Methanogens Group 32 Archaealsulfate reducers Group 33 Extremely halophilic, archaeobacteria(halobacteria) Group 34 Cell wall-less archaeobacteria Group 35Extremely thermophilic and hyper- thermophilic S⁰-metabolizers

Degradation of complex organic pollutants in the butane digesterpreferably requires the interaction of microbial populations(consortia). Butane or alkane-utilizing bacteria may degrade pollutantsaerobically (or anaerobically) through direct metabolism, sequentialmetabolism, reductive metabolism, dehalogenation, or cometabolism.

The requirement for a controlled environment and biological communitymay dictate the design of treatment facilities and the kinetics ofbiological growth. Typically, during conventional wastewater treatment,bacterial growth can be expressed as the variation of the mass of themicroorganisms with time. Four phases have been used to describebacterial growth: the lag phase; the log-growth phase; the declininggrowth phase; and the endogneous phase.

The lag phase represents the time required for bacteria to acclimate totheir nutritional environment. Butane availability may shorten the lagphase by acclimating (and stabilizing) the microbial populations intheir environment. For example, by stabilizing the microbial populationsduring pulsed cycles of butane and air (or oxygen), the entire microbialcommunity may be better adapted for purification processes.

In the log-growth phase, there is excess food surrounding the organisms,and the rate of metabolism and growth is a function of the ability ofthe bacterial populations to process the substrate. Because of itssolubility, pulsed cycles of butane may adapt the microbial populationsto better utilize the excess of available carbon substrates (of varyingavailabilities) in the wastewater by acclimating (and stabilizing) themicrobial populations in the apparently nutrient-rich environment. Thisin turn will increase the microbial communities to process an increasednumber of available substrates. Butane may be pulsed to create feedingfrenzy/starvation cycles. During the starvation cycle, the increasedmicrobial populations (a larger percentage of the population containingbutane-utilizing bacteria) will be forced to consume and mineralize theremaining wastewater constituents, such as organic substrates possessingvarying microbial availabilities at biological rates that would exceedconventional treatment processes.

In the declining growth phase, the rate of increase of bacterial massdecreases because of limitations in the food supply. Butane availabilitywill reverse the effects of limitations in the food supply therebyincreasing the rate of bacterial mass. During conventional wastewatertreatment, the established microbial populations consume the mostreadily available carbon sources. As the readily available sourcesdiminish, the more recalcitrant carbon sources remain in the wastewatermix. This in turn causes a decrease in the bacterial mass. Butanepulsing offsets the effects of carbon source availability by reinforcingand strengthening the adapted microbial populations. The adaptedpopulations attack the remaining carbon sources during the starvationcycles with renewed vigor.

In the endogenous phase, microorganisms are forced to metabolize theirown protoplasm without replacement because the concentration ofavailable food is at a minimum. Butane availability will reverse theeffects of the endogenous phase. With butane pulses, the endogenousphase period will be drastically reduced and may occur (if at all)during the starvation cycles (of short duration).

EXAMPLE

Return activated-sludge (RAS) was collected from a municipal wastewatertreatment plant located in Massachusetts. The RAS was drawn from thereturn line of a settling tank (after treatment in an aeration tank) inan activated-sludge process municipal wastewater treatment plant. RASconsists of the mixture of old and new aerobic bacterial cells, whichhave settled out in the settling tank over a period of time. Theactivated-sludge was introduced into a bioreactor vessel comprisingaeration diffusers, a constant speed electric mixer with propeller, anair-supply pump, and vent line, as illustrated in FIG. 10. Thebioreactor 70 shown in FIG. 10 includes a containment vessel 71 with ascrew down cover 72 sealed with a gasket 73. A vent line 74 extendsthrough the cover 72. An impeller 75 mounted in the vessel 71 is rotatedby a motor assembly 76. An air supply pump 80 is connected to an airfeed line 81. A butane injection port 82 is connected to the air feedline 81. A diffuser 84 is connected at the end of the air feed line 81.

The reactor contained approximately five gallons of organic waste, whichconsisted of water with the addition of the return activated-sludge fromthe treatment plant. The return activated-sludge appeared to have theconsistency of slurry prior to the addition of water. Prior to thebutane injections, the solids were thoroughly mixed and a compositesample was drawn for analysis of total solids. The results aresummarized in Table 1 below. The constant speed mixer and aerationsystem were operated continually (200 liters per hour) with brief stopsevery hour to conduct butane injections (500 ml of n-butane). The butanewas injected into a syringe port connected to the air-supply line athourly intervals as shown on Table 1 and in FIG. 10 . After a period ofapproximately three days, the butane injections were halted. During thehour not shown in the table, the bioreactor was operated with aerationand mixing without butane injection.

On Day No. 1, a pretreatment composite sample was collected from thebioreactor after thorough mixing of the RAS with the propeller unit (2minutes). The sample was submitted to Rhode Island Analytical Laboratoryfor total solids analysis referencing EPA Method 160.3. The results aresummarized in Table 2 below.

On Day No. 5, a composite sample was collected from the bioreactor (postbutane treatment) and submitted to Rhode Island Analytical Laboratoryfor total solids analysis referencing EPA Methods 160.3. The results aresummarized in Table 1 below.

TABLE 1 Volume of Aeration Day No. Time Butane (200 L/hr) Mixing 1 19:00500 ml On On 1 20:00 500 ml On On 1 21:00 500 ml On On 2 08:00 500 ml OnOn 2 09:00 500 ml On On 2 11:00 500 ml On On 2 12:00 500 ml On On 213:00 500 ml On On 2 14:00 500 ml On On 2 15:00 500 ml On On 2 16:00 500ml On On 2 17:00 500 ml On On 2 18:00 500 ml On On 2 19:00 500 ml On On2 20:00 500 ml On On 3 10:00 500 ml On On 3 11:00 500 ml On On 3 12:00500 ml On On 3 13:00 500 ml On On 3 14:00 500 ml On On 3 15:00 500 ml OnOn 3 16:00 500 ml On On 3 17:00 500 ml On On 3 18:00 500 ml On On

TABLE 2 Day No. Total Solids (mg/1) Settleable Solids (ml/l) 1(Pretreatment) 2,200 329 5 (Butane Treatment) 1,900 (14% reduction) 158(52% reduction)

The RAS slurry immediately thinned (within 10 hours) after the butaneinjections. The RAS appeared less dense with a flocculant consistency.In addition, all odors associated with the RAS sludge sample were notdetectable by olfactory senses after the first three butane injectionsconducted on Day No. 1. Thus, butane may be used for odor control inwastewater and other industries.

On Day No. 3, the sludge was observed to rise in the bioreactor chamberand into the vent tubing. In addition, small diameter bubbles wereobserved at the liquid surface. We believe the bubbles were nitrogen gasgenerated during denitrification processes. As the nitrogen gas formedin the RAS, the sludge mass became buoyant and rose in the bioreactorchamber (rising sludge phenomenon). Since denitrification was believedto be an anaerobic process, this phenomenon was unexpected since theaeration process was operated continually during the process treatment.Although not intending to be bound by any particular theory, theprincipal biochemcial pathways of denitrification may not be anaerobicbut rather a modification of aerobic pathways. Alternatively, the butaneinjections may have increased oxygen demand to the point that exceededthe capacity of the aeration unit used for the study. Consequently, thebioreactor may have turned slightly anoxic. The bioreactor exampledescribed above only details the process and method conception.Optimization of the process (i.e., butane volume and flow rates) was notdetailed or considered.

In accordance with an embodiment of the present invention, butaneenhanced treatment of wastewater may be conducted as a modification ofexisting aeration tanks in municipal or chemical wastewater treatmentfacilities or as stand alone or ancillary treatment reactors. Manyvariations or process permutations exist or may be implemented using thealkane process. The process could be modified to pre-treat sludge, treatsludge on-line, treat return sludge, lower biological oxygen demand,total organic carbon or any other form of wastewater where solidsreduction, odor control or organics removal is desirable. The alkaneprocess may also be used to further treat sludge obtained from anaerobicdigestion processes. The process may be used to reduce solids in anytype of wastewater effluent. Furthermore, butane may be injected intowastewater early in the treatment process to abate nuisance odorsassociated with wastewater liquids/solids.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A method of treating wastewater comprisingintroducing at least one alkane into the wastewater.
 2. The method ofclaim 1, further comprising introducing oxygen-containing gas into thewastewater.
 3. The method of claim 2, wherein the oxygen-containing gasis introduced in the form of air.
 4. The method of claim 1, wherein theat least one alkane comprises butane.
 5. The method of claim 4, whereinthe butane stimulates the growth of butane-utilizing bacteria.
 6. Themethod of claim 5, wherein the butane-utilizing bacteria compriseaerobic bacteria.
 7. The method of claim 5, wherein the butane-utilizingbacteria comprise anaerobic bacteria.
 8. A method of treating materialcontained in wastewater, the method comprising: stimulating growth ofalkane-utilizing bacteria; and allowing the alkane-utilizing bacterialto degrade at least a portion of the wastewater material.
 9. The methodof claim 8, wherein the alkane-utilizing bacteria are grown in thewastewater.
 10. The method of claim 8, wherein the alkane-utilizingbacterial are grown by introducing butane into the wastewater.
 11. Themethod of claim 10, further comprising introducing oxygen-containing gasinto the wastewater.
 12. The method of claim 11, wherein theoxygen-containing gas is introduced in the form of air.
 13. The methodof claim 10, wherein the butane stimulates the growth ofbutane-utilizing bacteria.
 14. The method of claim 13, wherein thebutane-utilizing bacteria comprise aerobic bacteria.
 15. The method ofclaim 13, wherein the butane-utilizing bacteria comprise anaerobicbacteria.